1. Field
Example embodiments relate to a thin film transistor (TFT) and a method of manufacturing the same. Other example embodiments relate to a TFT that reduces leakage current, off current and/or contact resistance and a method of manufacturing the same. Yet other example embodiments relate to a TFT that may be used for a large-area high-resolution display device and a method of manufacturing the same.
2. Description of the Related Art
Thin film transistors (TFTs) may be used in various fields. For example, TFTs may be used as switching and driving elements in display applications and/or used as select switches for cross-point memory devices.
Liquid crystal displays (LCDs) are generally used as panels for televisions (TVs), although research is being conducted regarding the application of organic light emitting diodes (OLEDs) to TVs. Effort is directed toward the development of display devices for TVs that meet the demands of the market. The demands include larger area TVs or digital information displays (DIDs), lower prices and/or higher quality in features such as moving picture display, resolution, brightness, contrast ratio, color reproduction and the like. In order to meet the demands, TFTs, which can be used as switching and driving elements for large-area and high-performance display devices, may be necessary.
Amorphous silicon (a-Si) TFTs are generally used as driving and switching elements for display devices because the a-Si TFTs may be uniformly formed on a large substrate having a size of 2-m or more at a substantially low cost. As display devices are developed to be larger and to have higher quality, driving and switching elements that have a higher performance may be necessary. Because a-Si TFTs have a low mobility of about 0.5 cm2/Vs, there are limits to increasing the performance of the a-Si TFTs. As such, there is a demand for high-performance TFTs having a mobility higher than that of the a-Si TFTS and a method of manufacturing the high-performance TFTs.
Because polysilicon (poly-Si) TFTs may have a mobility of tens to hundreds of cm2/Vs and may be have a higher performance than a-Si TFTs, the poly-Si TFTs may be applied to high-quality display devices in terms of performance, unlike the a-Si TFTs. Also, poly-Si TFTs do not undergo as much characteristic deterioration as the a-Si TFTs.
It may be difficult to apply poly-Si TFTs to large substrates due to a complex manufacturing process and the inability to ensure uniform laser crystallization if polysilicon is formed. Excimer laser annealing is used as a low temperature method of manufacturing high-mobility poly-Si TFTs. However, laser equipment is expensive and there are limits to applying poly-Si TFTs to a large substrate using excimer laser annealing.
A super grain poly-Si (SGS) method has been used. The SGS method has substantially high quality and substantially high speed crystallization, as well as lower costs. The SGS method is difficult to stably drive TFTs due to substantially high leakage current and substantially high off current.